US teacher, a mother of twins, stabbed to death in Abu Dhabi shopping mall

A female American teacher was stabbed to death Monday in an Abu Dhabi mall only weeks after U.S. embassy in the Middle East warned of such attacks being planned.

The unidentified woman, who is a mother of twins, according to NBC News, was killed in a bathroom at a shopping mall on Reem Island. She was confirmed by the U.S. Embassy in the city to be an American citizen.

Surveillance footage from the mall shows the alleged attacker entering th mall and then the bathroom while wearing an all-black Niqab, traditional Muslim clothing that covers a woman from head-to-toe.

In a sign there may have been a person inside the mall who summoned the killer, the assailant rode an elevator to the top floor, spoke to a security guard and went directly to the bathroom.

People, including the believed attacker, were shown fleeing the bathroom after the stabbing, which, according to video timestamps, appears to have happened about 90-minutes later.

Sources told NBC News the stabbing happened during a fight in the restroom, and that the 37-year-old teacher was attacked "with a sharp tool."

"The injured woman was immediately rushed to Sheikh Khalifa Medical City where she succumbed to the wounds she sustained in the attack," Abu Dhabi police said in a statement.

The footage also showed the attacker leave the mall without being apprehended, despite a woman initially trying to confront him or her at the elevator.

The Good Samaritan quickly backed down and the killer vanished without a trace.

Police have very little clues as to the attacker's age, sex or nationality, they have admitted, but are working to track down suspects.

The dead woman's twins are now in police custody.

U.S. embassies and consulates across the region, on October 29, advised Americans in the region that such attacks could be imminent.

Anonymous postings to a known-terror website encouraged attacks against American teachers, the warning said.

At the time, the U.S. State Department admitted it was ""unaware of any specific, credible threat against any American or other school or individual in the United Arab Emirates."

Diplomatic officials said they were working with local school and authorities to isolate any plots, but advised Americans to "avoid crowds or large gatherings when traveling in public."